The invention pertains to an absorption material for use in an absorbent article such as a diaper, an incontinence protector, a sanitary napkin or the like. The invention further relates to an absorbent article comprising the absorption material.
Absorbent articles such as diapers, incontinence protectors, sanitary napkins, bed protectors, seat covers, or the like generally comprise an absorption body which is constituted by one or several layers of absorption material. Usually, the absorption material mainly consists of cellulose fluff pulp. When such an absorption body is wetted, the area of the absorption body which is first hit by liquid will absorb substantially all the liquid. Thereby, this area will be saturated with liquid and when subsequent wettings occur the absorption body will not have sufficient capacity in order to absorb all the emitted body liquid. As a result, liquid will flow out over the surface of the article and leak out past the edges of the article.
In order to overcome such leakage, it has been suggested to provide the absorption body with compression patterns of different kinds, thereby increasing the liquid distributing ability of the article. An example of such a compression pattern is grooves which extend in the longitudinal direction of the article. Since the finer capillaries in the compressed portions of the absorption body transport liquid better than surrounding portions of the absorption body, it is possible to obtain, in this manner, a certain degree of draining of the initially wetted area of the absorption body. However, the transportation of liquid is dependent on capillary action, which is a slow process, meaning that the draining of the wetted area will often be incomplete and insufficient.
Another way to reduce the risk of leakage, occurring as a result of the initially wetted area of an absorption body being saturated with liquid, is to increase the amount of absorption material in the acquisition area. Although it is possible to increase the leakage security of the article in this manner, such a solution still presents some drawbacks. When the absorption material consists of cellulose fluff pulp, an increased amount of absorption material will make the article thick and bulky in the acquisition area. Since the acquisition area of body-worn absorbent articles should be accommodated in the crotch portion of the wearer, between the legs of the wearer , such a thick and bulky article may be perceived as being uncomfortable to wear. In addition, it is difficult to conceal a voluminous article under ordinary clothing, which means that adult wearers, in particular, are reluctant to wear such articles since they are perceived As embarrassing.
An alternative way to increase the absorption capacity in the acquisition area is to use what is known as superabsorbent material, i.e. polymers having the ability to absorb liquid in an amount corresponding to several times their own weight. Such superabsorbents absorb liquid by chemically binding it in a gel. When absorption has taken place, the liquid remains in the gel and will not be transported any further. This implies that superabsorbent materials incorporated into an absorbent structure greatly reduce the liquid spreading in the structure and contribute to a poor utilization of absorption material which is positioned at a distance from the area which is initially hit by emitted body fluid.
Furthermore, concentrating the absorption material to the initially wetted area of an absorbent article means that liquid will remain in close contact with the body of the user. For this reason, such an article may be perceived as being wet and uncomfortable to wear after wetting, even if the absorption capacity of the article has not yet been fully used. Another drawback, in connection with liquid which remains in the vicinity of the body of the wearer, is that moisture from the article may cause irritation of the wearer""s skin.
One purpose of the present invention has been to offer a possibility of directing and controlling the absorption and the liquid distribution in an absorbent article of the kind mentioned in the introduction. A further purpose of the invention is to achieve an absorbent article having high leakage security and which makes better use of the available absorption capacity. An objective of the invention has also been to offer an absorption material which makes it possible to obtain controlled absorption and liquid distribution in an absorbent article.
An absorption material in accordance with the invention is primarily characterized in that the material comprises a carrier material exhibiting a coating of a thermosensitive polymer, which polymer exhibits a cloud point at a temperature in the vicinity of and somewhat below the body temperature of a healthy human being, wherein the surface structure and the chemical properties of the surface of the polymer change at the cloud point, whereby the absorption material substantially lacks absorption capacity at a first temperature on one side of the cloud point but exhibits good absorption capacity at a second temperature on the other side of the cloud point.
The thermosensitive coating on the absorption material in accordance with the invention implies that the temperature of the surroundings of the absorption material determines whether the absorption material is available for absorption. The thickness of the coating may be used in order to control the absorption characteristics of the absorption material and can, accordingly, be anything from a mono-layer of thermosensitive polymer to a thick coating.
When the absorption material is used in an absorbent article intended for absorption of body fluids, the temperature of the fluid which reaches the absorbent article will determine whether or not the fluid will be absorbed. Thereby, the thermosensitive material may either be of a kind which is non-absorbent at a temperature higher than the cloud point, but absorbent at a temperature below the cloud point, or vice versa. In both cases the cloud point should be somewhat below the body temperature of a healthy human being, in the first instance preferably 2-7xc2x0 C. below and most preferably 2-3xc2x0 C. below. In the second instance the cloud point may be a few centigrades further below, whereby absorption will continue during a longer period of time while the body fluids are cooling down.
Accordingly, the cloud point should be between 28xc2x0 C. and 35xc2x0 C., and preferably between 32xc2x0 C. and 34xc2x0 C.
Thermosensitive polymers having suitable properties are, for instance, derivatives of cellulose such as ethylhydroxyethyl cellulose (EHEC). Other suitable polymers are acrylamides such as poly-n-isopropyl acrylamide (PNIPAM), poly-n-n-methacrylamide, poly-n-n-propyl methacrylamide and poly-n-n-diethyl acrylamide. Another large family of polymers having cloud points lying within the temperature ranges which are suitable for the present purpose are polyethylene glycols and co-polymers thereof. Furthermore, branched polymers containing ethyleneoxide blocks may be used.
The carrier material comprised in the absorption material may consist wholly or partly of fluffed cellulosic fibres or of superabsorbent material in the form of particles such as flakes, fibres, grains, granules or the like.
In addition, the coated absorption material may consist of a combination of superabsorbent material and fluffed cellulose fibres, or other absorbent fibres such as cotton, viscose, or the like. It is further possible, in accordance with the invention, to coat non-absorbent, hydrophobic fibres with a thermosensitive polymer. An absorbent material of this kind will preferably have no absorption capacity when it is first wetted by body fluid, but will be able to absorb small quantities of residual fluid when the temperature of the fluid decreases below the cloud point of the polymer. Material of this kind may be used as liquid-permeable acquisition and distance layers between a covering layer and an absorption body of an absorbent article, or may be a component in the liquid-permeable covering layer of the article. Even if the fibrous structure is comparatively hydrophobic, small amounts of liquid may be retained between the fibres after wetting. An advantage of using a material in accordance with the invention close to the surface of an absorbent article is that the surface dryness of the article between wettings may be considerably improved.
The absorption material may be provided in the form of a bonded or unbonded fibre mat, in the form of a multilayered structure with mutually different material composition and/or different absorption properties.
In accordance with the invention, an absorbent article such as a diaper, an incontinence protector, a sanitary napkin or the like, exhibiting an absorption body enclosed in a partially liquid-pervious cover, is primarily characterized in that the absorption body comprises absorption material which comprises a carrier material exhibiting a coating of a thermosensitive polymer, which polymer exhibits a cloud point at a temperature in the vicinity of and slightly below the body temperature of a healthy human being, wherein the absorption properties of the polymer change at the cloud point so that the polymer substantially lacks absorption capacity at a first temperature on one side of the cloud point, but exhibits good absorption capacity at a second temperature on the other side of the cloud point.
In accordance with the invention, the absorption body of the absorbent article may be constituted in a number of different ways. A cover for an absorbent article of the intended kind is generally constituted by a liquid-permeable layer and a liquid-impervious layer which are mutually connected around the absorption body of the article and together enclose the absorption body. According to one embodiment of the invention, the absorption body in such an article may thereby comprise a first absorption layer arranged closest to the liquid-permeable layer and mainly consisting of the absorption material coated with the thermosensitive polymer, and a second absorption layer arranged closest to the liquid-impervious layer and mainly consisting of absorbent material without thermosensitive coating.
According to another embodiment, the absorption body comprises an absorption layer exhibiting longitudinal bands, wherein bands mainly consisting of the absorption material coated with the thermosensitive polymer alternate with bands mainly consisting of absorbent material without thermosensitive coating.
The absorption material coated with the thermosensitive polymer is preferably primarily arranged at the crotch portion of the article.